1. Field of the Invention
The invention relates to an engine control system with a motorized butterfly body for a motor vehicle internal combustion engine equipped with a fuel injection system.
2. Description of the Prior Art
In the most conventional fuel injection systems currently equipping motor vehicle spark ignition internal combustion engines, at least one shut off member, termed butterfly, mounted so that it can pivot on a spindle in a duct of a butterfly body is connected to the accelerator pedal by a cable-operated mechanical transmission making it possible to regulate the angular position of the butterfly in the duct in order to cause the flowrate of intake air to the engine to vary, as a function of the demand from the driver. Simultaneously, modern spark ignition engines are equipped with an electronic control and monitoring unit, termed engine control unit, which comprises a computer and which has the function of controlling and monitoring the operation of the ignition circuit and of the fuel injection circuit of the engine. This engine control unit is connected to several sensors for sensing operating parameters of the engine, from which it receives signals which represent in particular the engine speed, the position of the shaft of the engine, the air pressure in the intake manifold, as well as possibly the temperature of the air and the temperature of the water in the cooling circuit, without this list being limiting. On the basis of the signals received from the sensors to which this engine control unit is connected, as well as possibly on the basis of data recorded in memories of this unit, the latter formulates orders for controlling the ignition and injection circuits, which it transmits to actuators of these circuits, such as the windings of injectors, a fuel pump, and ignition coils, in order to activate them. So that the operation of the ignition and injection circuits can be controlled suitably, under certain configurations of use of the engine, particularly during cold starts and when operating at low idle, as well as in a way which is coherent with the control of the air supply circuit, so that it results from the demand from the driver, the angular position of the butterfly is detected by a sensor transmitting a corresponding signal to the engine control unit, which takes this signal into account not only to formulate the control signals which it transmits to the actuators of the ignition and injection circuits, but also to formulate a control signal which it transmits to an actuator, such as an electric stepper motor for maneuvering a valve, mounted in an air intake circuit as a bypass round the butterfly, for the phases for which the engine is starting-up and operating at low idle.
Moreover, it is also known how to equip motor vehicles with installations for safety or driver comfort, for example with a system for preventing wheelspin, a system for preventing the wheels from locking up, or even with a system for setting the speed of the vehicle to a speed chosen by the driver. Each of these systems also comprises an electronic control and monitoring unit, which receives information from appropriate sensors, witnessing the operating state of the vehicle and of some of its components, and which prepares, on the basis of this information, control orders transmitted to appropriate actuators. For each of the particular systems mentioned hereinabove, one of the appropriate actuators is an actuator, for example an electric motor, which regulates the angular position of the butterfly, in parallel with the mechanical control by means of cable connecting this butterfly to the accelerator pedal, the actuator for the system preventing wheelspin or for the antilock system having, for obvious reasons of safety, priority over the control exerted by the driver by action on the accelerator pedal.
However, outside the periods for which the safety systems (antiwheelspin, antilock) intervene, the regulation of the air taken in remains under the direct control of the driver, through his action on the accelerator pedal. This leads, in particular, to an engine torque which is controlled to a greater or lesser extent at the driving wheels, as well as to a variable behavior of the vehicle during transient conditions. In order to overcome this drawback it has been proposed to substitute for the mechanical transfer law between the position of the accelerator pedal and the position of the butterfly, a programmable transfer law, incorporating a function for dynamic correction of the butterfly as well as a function for controlling the progressive nature of its angular movement, and finally a setting of the low idle speed. It has consequently been proposed to install, between the accelerator pedal and the butterfly, an additional control and monitoring unit including a computer, as well as an additional actuator, such as an electric motor, the additional control unit receiving a signal from a sensor for sensing the angular position of the accelerator pedal and formulating, taking account of this signal, a signal for controlling the actuator, which maneuvers the butterfly.
In order to simplify such an installation which comprises, for maneuvering the butterfly, at least two different actuators, one of which, controlled directly by the engine control unit, comes into play during cold starts and for setting the low idle speed, and the other of which is an actuator controlled from the control unit and sensitive to the position of the accelerator pedal, and calling upon the functions of dynamic correction and progressiveness, to which there may be added a third or even a fourth actuator belonging respectively to the system for setting the speed and the system for preventing wheelspin, it has recently been proposed to regulate the position of the butterfly with the aid of a single actuator, itself controlled by its own electronic control and monitoring unit, termed control unit of the butterfly, formulating the transfer law between the position of the accelerator pedal and that of the butterfly, not only on the basis of a signal for recopying the angular position of the accelerator pedal, this signal being received from a corresponding sensor, but also of a signal received from the engine control unit, to which the control unit of the butterfly is connected by a communication line, as well as of signals received from appropriate contactors, for example of the system for setting the speed of the vehicle, in order to place the butterfly in a position making it possible to maintain the chosen speed, and possibly from the system for preventing wheelspin, in order to close the butterfly again if need be.
Furthermore, in such an installation, the single actuator for the butterfly and the sensor for sensing the angular position of the butterfly have already each been incorporated into the butterfly body.
In this case, the control unit of the butterfly is directly connected, on the one hand, to the actuator of the butterfly, which it controls by means of an electronic power circuit and, on the other hand, to the sensor for sensing the angular position of the butterfly, originating from which a signal about the angular position of the butterfly is received by a circuit for automatically controlling the butterfly in terms of position, this circuit being provided in the control unit of the butterfly in order to compare the said signal about the angular position of the butterfly with at least one position reference signal and in order to formulate, on the basis of an error signal resulting from this comparison, an order for regulating the position of the butterfly, which is transmitted to the power circuit.
The drawback of such an installation is that the control of the butterfly is provided for solely by the control unit of the butterfly, so that any failure of this unit, or of the communication line via which it receives information from the engine control unit, is a factor detracting from safety. This lack of safety as regards closure of the butterfly, in order to decrease the power of the engine, is found also as regards the monitoring of the demand from the driver, which is provided for solely by the sensor for sensing the position of the accelerator pedal, this being directly connected to the control unit of the butterfly. Likewise, the monitoring of the position of the butterfly is provided for solely by the corresponding sensor, directly connected to the control unit of the butterfly.